Surgical sutures are currently attached to needles primarily by inserting one end of the suture into either a channel or a drilled hole in the blunt end of the needle and then mechanically swaging the channel or hole onto the suture so that the latter is held firmly and so that it requires a substantial amount of force to detach the needle from the suture.
This method of attachment suffers from the disadvantage of requiring that the channels or holes be made with great precision, necessitating expensive machinery and skilled labor. A second disadvantage in this method of attachment is that the swaging operation is performed on precision machinery which requires frequent adjustment and replacement of expensive dies by skilled mechanics.
A second method of attaching surgical sutures to needles (used primarily with needles and sutures of small diameter) involves applying a suitable liquid adhesive to the end of the suture before inserting the suture end into a hole in the blunt end of the needle. Proper curing or hardening of the liquid adhesive compound holds the suture firmly in place.
One disadvantage of the adhesive method is that the liquid adhesive compound does not always fill the hole around the suture either because of failure to displace the air in the hole, or because of bubbles in the adhesive. This results in weakened bond strength after curing.
A second disadvantage of the adhesive system of attachment of sutures to needles is that the suture, after insertion into the hole, may be inadvertently dislodged from the hole (either partially or completely) while the needle suture combination is being arranged on a curing tray.
Another disadvantage is that the adhesive compound may not always cure to proper hardness and may thus produce a weakened bond.
Finally, still another disadvantage is that the surfaces of the hole and of the suture tip must be specially prepared to promote adhesion to the adhesive. Such special preparation adds to the cost of providing attachment in this manner.
U.S. Pat. No. 1,558,037, issued to Harry D. Morton on Oct. 20, 1925, discloses a method of attaching a suture to a recess in the blunt end of the needle, which recess is constricted at its neck and enlarged in its interior. The Morton patent discloses filling the excess space around the suture tip with an adhesive material; and alternatively, discloses that some "readily softening suture materials," such as catgut, soften and expand when wet and can thus expand in the presence of water to fill the large portion of the hole. The Morton patent states that such expansion is sufficient to ensure sufficient anchoring of catgut without an adhesive.
The Morton patent discloses that the suture end, upon wetting, expands in diameter and, upon hardening, has a diameter larger than before being wetted. It does not state that the diameter, upon hardening, is as great as it was when wetted, and indeed, it is not because catgut and other collagen materials shrink upon drying, the amount of such shrinking being dependent on the degree of tanning of the collagen. Thus, the suture tip in the Morton method of attachment will, upon drying, be smaller than the enlarged space in the hole and will not be in intimate contact wth the surfaces of the hole.
U.S. Pat. No. 1,665,216 issued to Morton et al on Apr. 10, 1928 discloses a method for permanently anchoring catgut suture within a needle recess by utilizing a unique property of catgut, i.e., the ability of catgut to expand into a hard and tough horn-like material upon heating. According to this reference, the expansion of catgut is permanent, the heat appearing to produce a marked change in the structure of the catgut, rendering the same hard, tough and horn-like. The catgut reportedly expands with considerable pressure against the wall of the recess which renders it particularly resistant to attempts to withdraw the suture from the recess. In effect, this reference discloses a method for the permanent attachment of catgut which is an alternative to the mechanical methods of attachment described in the prior art.
The security of attachment of eyeless needles to surgical sutures is prescribed in the U.S. Pharmocopoeia, Vol. XVIII at Page 944. It has been the practice of suture manufactures in the United States and abroad to securely attach the suture to the needle by swaging, with an adhesive, or by other methods so that the minimum pull-out standard recited in the U.S. Pharmacopoeia is met or exceeded.
It has recently been found useful to use needle-suture combinations in which the needle and the suture are readily separable from each other by a sharp tug. Several methods have been devised for preparing needle-suture combinations in which the pull-out values, or the force required for separating the needle from the suture by a straight pull, is within a controlled range, usually less than 30 ounces and preferably between 3 and 26 ounces.
One approach to controlling suture pull-out values is described in co-pending application Ser. No. 516,549, filed Oct. 21, 1974. This approach involves swaging the needle to provide a controlled degree of compression to the end of the suture within the needle recess. This approach is restricted to needle-suture combinations wherein the suture is of large size, i.e., size 4/0 and larger (diameter greater than 7.0 mils), and produces average pull-out values of 3 to 26 ounces, indicating that it takes a straight pull of the magnitude within that range to separate the needle from the suture.
Another approach to the problem is described in U.S. Pat. No. 3,875,946. In this approach sufficient tension is applied to the suture in a swaged needle-suture combination to move the suture relative to the needle recess and the tension is released when the force drops to the range desired for the pull-out value, the range varying for different sizes of suture. This approach is applicable to a broader range of suture sizes than the approach of application Ser. No. 516,549, and is applicable to sizes as small as 8/0.
The present invention provides another method for attaching needles to sutures formed of certain synthetic polymeric materials which provides for the removal of the needle by the application of a controlled amount of pulling force.